The present invention relates to controlling an image signal in a moving picture transmission and reception system, and more particularly, to a device and method for controlling a brightness of an image signal in a moving picture transmission and reception system.
A moving picture transmission/reception system is implemented with a transmission unit and a reception unit. The transmission unit converts an optical energy sensed by a camera into an electric signal and transmits the signal after either an analog or digital signal processing, and coding. The reception unit then displays a moving picture through a reverse process of the transmission unit. However, an object in the image displayed through the above process may appear differently from the actual object. Also, it is sometimes necessary to display the original image in a form altered by a person or device. In such case, various post-processing methods must be used before displaying the image.
A method in the related art for controlling a brightness of an image in a moving picture transmission/reception system will be explained with reference to the figures. Particularly, FIG. 1 illustrates a flow chart of a process for equalizing a histogram to control a brightness of an image signal in this context. FIGS. 2A and 2B show an example of a histogram and a cumulative density function (CDF) curve obtained from a relatively dark image according to a related art while FIGS. 2C and 2D show an example of a histogram and a CDF curve obtained from a relatively bright image according to a related art.
Referring to FIG. 1, a method for controlling a brightness of an image in the related art begins by calculating a histogram of the brightness signal in one frame of the input still image as in FIGS. 2A and 2C, and then calculating a CDF of the histogram as in FIGS. 2B and 2D. Thereafter, a contrast conversion is executed by scaling the ordinate, i.e. the number of pixels, of the CDF curve to fit within a range of 0xcx9c255 and using the scaled ordinate as a transfer characteristic.
However, when a luminance signal is expressed in 8 bits, the above method in related art becomes substantially cumbersome in that 256 counters are required to calculate and store a histogram, to thereby control the brightness.
Accordingly, an object of the present invention is to solve at least the problems and disadvantages of the related art.
An object of the present invention is to provide a device and method for efficiently controlling a brightness of an image in a moving picture transmission/reception system.
Another object of the present invention is to provide a device and method for controlling a brightness of an image in a moving picture by controlling a partial or an overall brightness of an image based upon the brightness of the image.
Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention. The objects and advantages of the invention may be realized and attained as particularly pointed out in the appended claims.
To achieve the objects and in accordance with the purposes of the invention, as embodied and broadly described herein, a device for controlling a brightness of an image signal according to one embodiment of the present invention includes a control point detecting unit which receives an image and obtains a CDF of a frame of the image, divides an abscissa of the CDF into a required number of portions, and detects control points resulting from the division; and an image signal brightness controlling unit which calculates a change in a brightness of a frame of the image based upon the CDF and the control points. The device may further comprise a frame buffer which stores an input frame while the control point detecting unit obtains a CDF and control points of the input frame such that the image signal brightness controlling unit calculates a change in brightness of the input frame from the frame buffer based upon the CDF and control points of the input frame. Alternatively, the control point detecting unit may obtain a CDF and control points for a nth frame of the image; and the image signal brightness controlling unit may calculate a change in brightness of a nth frame of the image based upon the CDF and control points obtained using a (nxe2x88x921)th frame of the image.
In another embodiment of the present invention, a device for controlling a brightness of an image signal includes a control point detecting unit which obtains a CDF of a frame of an input image, divides the CDF into a required number of portions, and detects control points resulting from the division to output a plurality of comparison signals and to set latch values; and an image signal brightness controlling unit which calculates a change in a brightness of the frame of the input image based upon the plurality of comparison signal from the control point detecting unit and based upon latch values set using a CDF of a previous frame of the input image.
In the above embodiment, the control point detecting unit includes a comparing unit which compares a plurality of most significant bits (MSBs) of the input image to a plurality of preset values and outputs the plurality of comparison signals; a first counting unit which counts the total number of pixels in the frame of the input image; a second counting unit which counts each of the plurality of comparison signals from the comparing unit according to a clock p_clk; a normalizing unit which selects each one of the count values from the counting unit in response to a count control signal count_control and multiplies a selected count value with a quotient from the maximum range or value of brightness divided by the number of pixels in the frame of the input image to output corresponding normalized count values; a latching unit which latches a plurality of stored latch value signals; and a latch value setting unit which sets a plurality of latch values based upon the normalized count values.
The latch value setting unit may include a signal selector which selects one of the plurality of preset values in response to the count control signal count_control; a first adder which adds a selected preset value to a normalized count value from the normalizing unit; a multiplier which multiplies a scaling signal hm_scale with a first sum from the first adder; and a second adder which adds the selected preset value to a signal from the multiplier and outputs a second sum as a latch value. Alternatively, however, the latch value setting unit may include a second signal selecting unit which selects one of either the latch value from the second adder or a preset latch value, in response to a user selecting signal user_select, and stores the selected latch value in the latching unit. This allows a brightness control of a partial region in a frame of a image.
Also, the image signal brightness controlling unit includes a signal selection logic unit which performs a selection logic in response to a comparison signal from the comparing unit and forwards a selection logic signal; a signal selector which selects at least one latch value signal in response to the selection logic signal; a first multiplier which multiplies a plurality of least significant bits (LSBs) of the image with a first signal from the signal selector; an operator which subtracts the six LSBs of the image from a preset value; a second multiplier which multiplies a second signal from the signal selector with a signal from the operator; an adder which adds the signals from the first and second multipliers; and a shifter which shifts a signal from the adder.
A method for controlling a brightness of an image in accordance to the present invention includes obtaining a CDF of a frame of the input image, dividing an abscissa of the CDF into a required number of portions, and detecting control points resulting from the division; and calculating a change in a brightness of a frame of the image based upon the CDF and the control points. The method may include storing an input frame while obtaining a CDF and control points of the input frame and then calculating a change in brightness of the input frame based upon the CDF and control points of the input frame. Alternatively, the method may obtain a CDF and control points of a nth frame of the image, but calculate a change in brightness of a nth frame of the image based upon the CDF and control points obtained using a (nxe2x88x921)th frame of the image.
Another embodiment of the method for controlling a brightness of an image signal in accordance with the present invention includes obtaining a CDF of a frame of an input image, dividing the CDF into a required number of portions, and detecting control points resulting from the division to output a plurality of comparison signals and to set latch values; and calculating a change in a brightness of the frame of the input image based upon the plurality of comparison signals from the control point detecting unit and based upon latch values set using a CDF of a previous frame of the input image.
The CDF may be obtained by comparing a plurality of MSBs of the input image to a plurality of preset values and outputting the plurality of comparison signals; counting a number of pixels in the frame of the input image; counting each of the plurality of comparison signals according to a clock p_clk; normalizing the count values by selecting each one of the count values from the counting unit in response to a count control signal count_control and multiplying a selected count value with a quotient from the maximum range or value of brightness divided by the number of pixels in the frame of the input image to output corresponding normalized count values.
Also, the latch values may be set and stored based upon the normalized count values. Namely, the latch values may be set by selecting one of the plurality of preset values in response to the count control signal count_control; adding a selected preset value to a normalized count value and outputting a first sum; multiplying a scaling signal hm_scale with the first sum; and adding the selected preset value to a product value and outputting a second sum as a latch value to be stored. Alternatively, setting the latch values may include selecting one of either the calculated latch value or a preset latch value, in response to a user selecting signal user_select, and storing the selected latch value.
Finally, the brightness of a frame may be calculated by performing a selection logic in response to a comparison signal and forwarding a selection logic signal; selecting at least one latch value signal in response to the selection logic signal; multiplying a plurality of LSBs of the input image with a first selected latch value signal; subtracting the plurality of LSBs of the image from a preset value; multiplying a second selected latch value signal with a signal resulting from the subtraction; adding the signals from the two multiplications; and shifting the resultant signal.